Question: $\text A = \left[\begin{array}{rr}3 & 5 \\ -1 & 1\end{array}\right]$ What is the determinant of $\text A$ ?
The determinant of a 2x2 matrix can be computed the following way: $ \left|\begin{array}{rr}a & b \\ c & d\end{array}\right| = (a \times d)-(b \times c) $ In this specific case, $ \left|\begin{array}{rr}3 & 5 \\ -1 & 1\end{array}\right| = (3 \cdot 1)-(5 \cdot -1) $ $ = 8 $